On 2013-01-01, Steve B wrote:
Let's say that I change my setting for either aperture, speed, or manual
priority.

I set the aperture for depth of focus, and the camera selects the speed.
I set the speed to freeze motion, and the camera selects the aperture.
I put it on manual, and can set both, even intentionally off if I want to.

Now, the question. I turn on the flash.

Does the camera use the settings I put in, or does it go into control of the
camera, and change any of the settings? I have taken many photos of the
same thing at many various settings, and I do know the photos come out
differently. I was just wondering about this part of the camera's actual
functioning.

What camera? Is it film or digital? Who made it? Most of the
following assumes digital -- and in particular the auto-adjust ISO --
film comes with one ISO only -- to change ISO, you change film -- or
change the developing times for the whole roll as a lump.

The Nikon D300s (and other DSLRs) takes a pre-flash to determine
exposure -- and will fire the flash just as much as is needed for the
settings. You left out one other variable for digital cameras -- the
ISO of the sensor, which can be set to automatic, so you can select both
shutter speed and aperture beforehand and it will try to adjust the ISO
to a value which allows a reasonable exposure.

Add an external flash, such as the SB-800 (for the above Nikon
DSLRs), and you have more flash power, but again built-in metering --
and the ability to remotely trigger the flash from the camera without
cables.

However -- if the external flash is not one built into the
camera or designed for remote control by the camera, like the SB-800,
you will need to adjust the aperture and exposure to the flash -- or
with some of the fancier flashes, select aperture, ISO, and such on the
flash's built in computer to go with the camera's settings.

Note, BTW, that electronic flash can't be used with some cameras
at higher shutter speeds (assuming a focal plane shutter), because the
camera's shutter is an opening traveling across the film (or sensor) --
or vertically over the film, so any particular area is exposed only for
the time selected, but the whole film is not uncovered at the same time
until you drop to something like 1/60th or 1/30th of a second, then the
flash fires during the time when the whole film is exposed at once.

The Nikon D70 and D300s (and likely their other DSLR models) has
a two-part shutter -- a mechanical shutter which opens in front of the
sensor, and then an electronic one which stays opaque until just the
right time, then goes transparent and back to opaque -- so this will
work with higher shutter speeds.

I apologize for the basic question, but I want to learn this from the ABC's
up, and I have a few missing letters.

There are rec.photo newsgroups which vary with what kind of
camera they are discussing. The right one of these for your camera
might be the best place to ask this. But be prepared to tell them what
camera you have.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---